Descriptions in this application are based on a wireless communications system, however the statistical multiplexing suggested in the application may be applied to a wired communications system as well as the wireless communications system without any change.
In order to point out clearly which parts or concepts are developed or improved in the present invention in comparison with the prior art, a prior art is described on the basis of communications system IS-95, which is already in service.
A first communication station and a second communication station in this application correspond to a base station and a mobile station in a conventional system. One first communication station communicates with a plurality of second communication stations and the present invention suggests a statistical multiplexing, which may be applied to a synchronized channel group having an orthogonality from the first communication station toward the second communication stations. For a system, which maintains the orthogonality only for each channel group, such as Quasi-Orthogonal Code (QOC) adapted to Code Division Multiplexing Access (CDMA) 2000, which is one candidate technique for a next generation mobile communications system, referred herein as “the IMT-2000 (International Mobile Telecommunications-2000)”, the present invention may be independently implemented for each channel group. Moreover, when classifying channels of the first communication station such as sectored or smart antenna systems into channel groups having the same send antenna beam, the present invention may be independently implemented in each channel group.
In the OCDM (Orthogonal Code Division Multiplexing) communications method adapted by the conventional IS-95 system, the first communication station allocates orthogonal code symbols, which have not been allocated among the orthogonal codes when establishing a call, to one of the second communication stations and the second communication station gives back the allocated orthogonal code symbols to the first communication station when releasing the call, such that other second communication stations may use the orthogonal code symbols.
In description of the prior art, same reference number is used for a component having same function as that of the present invention.
FIG. 1 shows a system according to both the prior art and the present invention. As shown in the figure, each communication channel 121, 122, 123 from the first communication station 101 to the second communication stations 111, 112, 113 is synchronized with maintaining orthogonality.
FIG. 2a shows configurations of a transmitter of the first communication station, which corresponds to a common element of the prior art and embodiments of the present invention. FIG. 2b shows configurations of the transmitter of the first communication station for a traffic channel of the prior art.
A pilot channel 200 is used as a reference signal for initial synchronous detection and tracking and synchronous decoding in the second communication station of FIG. 1. The pilot channel 200 is commonly used in all second communication stations in an area covered by the first communication station. The pilot channel 200 provides a phase reference for the synchronous decoding by transmitting symbols having a known pattern without passing through channel coding and channel interleaving as shown in FIG. 2a. 
A synchronous channel 210 is a broadcast channel which is one-sidedly transmitted to all second communication stations in an area covered by the first communication station, like the pilot channel 200. The first communication station transmits information (e.g. visual information, an identifier of the first communication station, etc.), which the second communication stations commonly require, to the second synchronous channel 210 through the synchronous channel 210. The data from the synchronous channel 210 pass through a convolutional encoder 214, a repeater 216 for adjusting a symbol rate, a block interleaver 218 for correcting an error burst and a repeater 219 for matching a send data symbol rate and are then transmitted to a spreading and modulating unit, shown in FIG. 3 and described below.
A paging channel 220 is a common channel used in case of an incoming message to the second communication station or for answering a request of the second communication station. A lot of paging channels 220 can exist. The data transmitted to the paging channel passes through a convolutional encoder 224, a symbol repeater 226 and a block interleaver 228 and passes through an exclusive OR gate 236 together with an output of a long code generator 232 generated by a long code mask 230. The data through the exclusive OR gate 236 is then transmitted to the spreading and modulating unit of FIG. 3.
A traffic channel 240 in FIG. 2b is a channel dedicatedly allocated to each second communication station for use until the call is completed. When there are data to be transmitted to each second communication station, the first communication station transmits the data through the traffic channel 240. The data from the traffic channel 240 passes through a cyclic redundancy check (CRC) 241 for inspecting an error in a specific time unit, or frame, (e.g. 20 ms in IS-95). Tail bits 242 are inserted into the traffic channel, all of which are “0”, and the data through the CRC 241 passes through a convolutional encoder 244 to ensure the independent encoding of the channel in a frame unit. The data then passes through a symbol repeater 246 to match the transmission data symbol rate according to a send data rate. After passing through the symbol repeater 246, the data passes through a block interleaver 248 to change an error burst into a random error. The data passing through the block interleaver 248 are scrambled in a scrambler 256 with use of a pseudo-noise (PN) sequence, generated by passing an output of a long code generator 232 decimated in a decimator 234 with the use of a long code mask 250 generated by an electronic serial number (ESN) allocated to each second communication station. A PCB (page control block) position extractor 258 extracts a position where a command for controlling transmission power from the second communication station is inserted in the PN sequence decimated in the decimator 234. A punch and insert 260 punches a data symbol corresponding to the insert position of the power control command extracted by the PCB position retractor 258 among the data symbols scrambled in the scrambler 256 and inserts the power control command, and then transmits the power control command to the spreading and modulating unit shown in FIGS. 3a-3c. 
FIGS. 3a, 3b and 3c show an embodiment of a spreading and modulating unit according to the prior art.
FIG. 3a corresponds to the commonly used IS-95 method employing BPSK (Binary Phase Shift Keying) as a data modulating method. FIG. 3b shows the spreading and modulating unit employing QPSK (Quadrature Phase Shift Keying) as a data modulating method for transmitting double data in comparison with the method in FIG. 3a. 
FIG. 3b illustrates the CDMA 2000 method, which is a candidate technique for the IMT-2000. FIG. 3c shows a spreading and modulating unit, which employs QOC (Quasi-Orthogonal Code) used in CDMA 2000, which is also a candidate technique for the IMT-2000. In FIG. 3, signal converters 310, 326, 330, 346, 364 convert logic signals “0” and “1” into physical signals “+1” and “−1” to be transmitted. Each channel of FIG. 2 passes through the signal converters and is then spread in spreaders 312, 332 by an output of a Walsh code generator 362. Transmission power of each channel is adjusted in amplifiers 314, 334. All channels of the first communication station are spread in spreaders 314, 334 by an orthogonal Walsh function of the Walsh code generator 362 fixedly allocated to each channel. The channels are then amplified in the amplifiers 314, 334 and then pass through QPSK spreading and modulating units 318, 338. Signals spread and modulated in the QPSK spreading and modulating units 318, 338 are multiplied by a carrier in multipliers 322, 342 to transmit to a sending band through low-pass filters (LPF) 320, 340. The signal multiplied by the carrier passes through a radio communication unit and is then transmitted through an antenna, not shown in the figures.
FIG. 3b is identical to FIG. 3a except that, in order to transmit the signal generated in FIG. 2 to QPSK instead of BPSK, different information data are carried in an in-phase channel and a quadrature phase channel through a demultiplexer 390. Using the demultiplexer 390 and the signal converters 310, 330 enables QAM (Quadrature Amplitude Modulation) as well as QPSK.
FIG. 3c shows the case that a QOC mask is used for distinguishing a channel from the first communication station to the second communication stations. Orthogonality is not maintained in a code symbol group using different QOC masks but maintained in a code symbol group using same QOC mask. Therefore, the present invention is applied to the orthogonal code symbol group using same QOC mask, which may maintain the orthogonality.
FIGS. 4a, 4b and 4c show signals used in the code division multiplexing, which spreads the signal generated in FIG. 2 and FIG. 3 into the orthogonal code symbol fixedly allocated to each channel, according to the prior art. A pilot channel 410 is spread by a fixedly allocated orthogonal Walsh code symbol W#0 in a spreader 412. Other channels are also spread by orthogonal Walsh code symbols W#1, W#2, . . . W#29, W#30, . . . W#63 fixedly allocated regardless of activities of the corresponding channels. If allocating the orthogonal code symbol fixedly to a channel such as channels 440, 450, 460 having relatively low transmission data activity, utilization of the orthogonal code, which is a limited source, is much less than 100%.
FIG. 4b shows how a despreading data symbol is spread by the orthogonal code. In reference numbers 471 to 477, white areas mean “0[+1]” and black areas mean “1[−1]”, for the Walsh code as an example of the orthogonal code.
FIG. 4c shows that the orthogonal code symbols are allocated to each channel in OCDM.
FIG. 5 briefly shows a configuration of a receiver of the second communication station corresponding to the transmitter of the first communication station according to the prior art. As shown in the figure, the signal received through the antenna passes through multipliers 510, 530 for multiplying the signal with a carrier, low pass filters (LPFs) 512, 532 for generating a baseband signal and short code generators 520, 540 for synchronizing the signal with a sequence same as the PN sequence used in the transmitter. The signal then passes through multipliers 514, 534 for multiplying the signal by the received baseband signal and then despreaders 516, 536 for accumulating the signals during a transmission data symbol area. A channel estimator 550 estimates a transmission channel by extracting only pilot channel components from the baseband signal as the orthogonal code symbol allocated to the pilot channel. A phase recovery 560 compensates phase distortion of the baseband signal with use of an estimated phase distortion value.
FIG. 6 shows a configuration of a receiver for a channel in which a control command for controlling transmission power from the second communication station to the first communication station like the paging channel is not inserted. Referring to the figure, maximum ratio combiners 610, 612 combine signals passing through the phase compensation to a maximum ratio. If the receiver performs QPSK data modulation as shown in FIG. 3b, the receiver performs descrambling by multiplexing the signal in a multiplexer 614, performing soft decision in a soft decision unit 616, then decimating an output of a long code generator 622 generated by a long code mask 620 in a decimator 624, and then multiplying the signal through the soft decision unit with a decimated result of the decimator 624. In the present invention, a configuration of a receiver in the second communication station for the orthogonal code hopping multiplexing is similar to the configuration in FIG. 6. For the synchronous channel, the descrambling processes 620, 622, 624, 626, 628 using the long code may be skipped.
FIG. 7 shows a configuration of a receiver to which a control command controls a transmission power from the second communication station to the first communication station like the traffic channel. As shown in the figure, the signal enduring the phase compensation in FIG. 5 passes through maximum ratio combiners 710, 712. In the case that a receiver performs a QPSK data modulation as shown in FIG. 5, a multiplexer 714 multiplexes an in-phase component and an orthogonal phase component in the signal. An extractor 740 extracts a signal component corresponding to the power control command transmitted from the first communication station among the received signal. The signal from the extractor 740 then passes through a hard decision unit 744 and is then transmitted to a transmission power controller of the second communication station. Data symbols, except the power control command in the received signal from the multiplexer 714, pass through a soft decision unit 742. A decimator 724 decimates an output of a long code generator 722 generated by a long code mask 720 generated by an identifier of the second communication station. The data symbols from the soft decision unit 742 are then multiplied in a multiplier 718 by a result of the decimator 724, so as to perform descrambling.
FIG. 8 shows a function of recovering the received signal through the signal processes of FIG. 6 and FIG. 7 from the first communication station, through block deinterleavers 818, 828, 838 and convolutional decoders 814, 824, 834. In a synchronous channel 810, in order to lower a symbol rate, a sampler 819 performs a symbol compression for the signals through the soft decision unit by accumulating the signals, which is an inverse process to the symbol repeater 219. The signal through the sampler 819 passes through a block interleaver 818. Then, a sampler 816 performs the symbol compression again for the signal, which is an inverse process to the symbol repeater 216, before the signal passes to a convolutional decoder 814. The signal enduring the symbol compression then passes through the convolutional decoder 814, recovering the synchronous channel transmitted from the first communication station.
In the case of a paging channel 820, the signal enduring the soft decision passes through a block deinterleaver 828 for channel interleaving. The signal enduring the channel interleaving passes through a sampler 826 for symbol compression according to the send data rate, which is an inverse process of the symbol repeater 226. The signal enduring the symbol compression passes through a convolution decoder 824 for channel decoding, recovering the paging channel transmitted from the first communication station.
In the case of a traffic channel 830, the signal enduring the soft decision passes through a block deinterleaver 838 for performing channel deinterleaving regardless of a send data rate. The signal enduring the channel interleaving passes through a sampler 836 for performing symbol compression according to the send data rate, which is an inverse process to the symbol repeater 246. A convolutional decoder 834 performs a channel decoding for the signal enduring the symbol compression. A tail bit remover 832 removes tail bits of the signal used for the independently send signal generated in a frame unit. A CRC 831 generates a CRC bit for the send data portion like the transmitter and inspects errors by comparison with a recovered CRC after channel decoding. If the two CRC bits coincide, the CRC 831 determines that there is no error, and then, the traffic channel data is recovered. If the transmitter does not include information about the send data rate in 20 ms frame unit, the send data rate of the first communication station may be determined by channel-decoding the signals enduring the independent channel deinterleaving and comparing the CRC bits. A system, which transmits a send data rate independently, just further requires a channel decoding process corresponding to the data rate.
In case of spreading the despreading data symbol by fixedly using the orthogonal code allocated when establishing a call as shown in FIG. 3 in order to maintain orthogonality between channels from the first communication station to the second communication station as shown in FIG. 1, the orthogonal code, limited source, may not be efficiently used for sending data having a relatively low activity, such as data indicated by reference numbers 440, 450 and 460 in FIG. 4a. In order to increase the activity of the orthogonal code with fixed allocation, rapid channel allocation and return are required. However, if transmitting the control signal information for channel allocation and return more frequently, more significant amounts of limited frequency resources should be used for the control information of the data transmission, not for the data transmission itself. Moreover, however rapid the channel allocation and return are processed, there should be a buffering process after the data to be transmitted reaches the first communication station until transmitted in order to transmit a channel allocation (or return) message and respond to the message. As the time for such processes is extended, more capacity is required in the buffer. Information, which requires checking whether the information is transmitted normally, should be buffered for retransmission. However, in the case of transmitting information without checking normal transmission of the information, such as, in a datagram method, a delay should be minimized in an allowable range in order to decrease the capacity of the buffer.
Therefore, while the prior art allocates the orthogonal codes in a fixed manner so as to have a 1:1 relation between the orthogonal code and the channel, the present invention, with a little modification of the prior art, performs statistical multiplexing for traffic channels having low activities in consideration of activity of the sent data in order to increase the activities of the orthogonal codes, which are limited resources, and to eliminate unnecessary channel allocating and returning processes in order to decrease the buffer capacity and data transmission delay.